The broad goal of the research proposed herein is an understanding of information processing differences between the left and right cerebral hemispheres in man and an understanding of the manner in which the two cerebral hemispheres interact. An attempt will be made to localize experimentally obtained hemispheric specialization or laterality effects precisely within a sequence of cognitive processing stages. To adequately accomplish this localization Same-Different reaction time experiments using verbal and nonverbal stimuli presented to various visual field locations are proposed to determine (a) whether the nature of the stimuli or the nature of the task to be performed using the stimuli is the primary determiner of results taken to indicate hemisphere differences and (b) whether the relative difficulty of perceptual and abstract-verbal processing stages is critically important in determining hemispheric advantage during a particular task.